In typical continuous processes utilizing a Raney nickel or Raney cobalt hydrogenation catalyst, the rate at which the catalyst is fed into the reaction medium must be carefully controlled. Active catalysts of that type are pyrophoric, however, and are therefore normally kept out of contact with air by transporting and storing the catalyst in a relatively inert liquid. Hence in some of the aforementioned processes, the rate at which the catalyst is fed into the reaction medium is desirably controlled by suspending the catalyst is such a liquid so as to disperse the catalyst substantially uniformly through the liquid in a known concentration of catalyst per unit volume of the suspension, and then controlling the volumetric flow rate of the suspension into the reaction mixture. Examples of processes in which the catalyst feed rate may be conveniently controlled in this way are described in U.S. Pat. No. 3,821,305 issued June 28, 1974 to G. Bartalini et al., the disclosure of which is incorporated herein by reference, and in U.S. Pat. No. 3,056,837 issued Oct. 2, 1962 to W. M. Steeman.
In processes such as that of U.S. Pat. No. 3,821,305 in which the reaction medium contains water, it may be also convenient to uniformly suspend the catalyst in water in the relative proportions in which the catalyst and water are desirably fed into the reaction medium and then control the feed rate of both water and catalyst by controlling only the volumetric feed rate of the resulting catalyst-in-water suspension. One difficulty encountered in use of a suspension of active Raney nickel or Raney cobalt catalyst in water, however, is that since such catalysts have relatively high densities, maintaining even very finely divided particles of the catalyst suspended in substantially uniform dispersion throughout the water typically requires an essentially constant and relatively vigorous stirring or other agitation of the suspension and, for reasons not fully understood, such agitation normally results in substantial foaming of the suspension. In many cases the foaming tendency is so severe that it presents a significant danger of loss of the pyrophoric catalyst by overflow from catalyst feed tanks. A technique for inhibiting such foaming is therefore very desirable and it is an object of this invention to provide such a technique for improvement of certain catalytic hydrogenation processes that involve suspending of a Raney nickel or Raney cobalt catalyst in an aqueous liquid for feeding of the catalyst into the hydrogenation reaction medium. Other objects of the invention will be apparent from the following disclosure in which all percentages are by weight except where otherwise noted.